The present invention relates an electroluminescence device and more particularly to an electroluminescence device using a highly moisture-resistant metal composite film as protective sheet for the opposite electrode.
The technological advancement in the field of electroluminescence devices (hereinafter referred to as ELDs) in recent years has made it possible to produce ELDs with relatively high luminosity and hence broadened the scope of application. Particularly, ELDs of dispersion type are attracting attention of interested parties as they have a wide variety of applications because of low cost, high luminosity and other advantages.
FIG. 3 of the accompanying drawings illustrates a sectional view of a conventional ELD and FIG. 4 is a partial enlarged view thereof, where reference numeral 1 denotes a transparent sheet, 2 a transparent electrode formed under said sheet 1 in the sense of the drawings, 3 a light emitting layer made of a phosphor-coated material and a dielectric material, 4 an opposite electrode made of a foil of metal such as aluminum, 5 a moisture absorbing layer having a highly hygroscopic property, 6 and 7 are protective sheets for protection of said transparent sheet 1, transparent electrode 2, light emitting layer 3, opposite electrode 4 moisture absorbing layer 5. Each of said transparent electrode 2 and opposite electrode 4 is provided with a lead terminal which is not shown in the drawings so that they can be electrically connected with an external power source and said light emitting layer 3 emits light when voltage is applied thereto.
Such a conventional ELD is normally sealed airtight by a pair of protective sheets 6 and 7, since if it is used in a moist environment, it can be degraded to significantly lose its luminosity and hence its durability as the phosphorcoated material in the ELD is decomposed quickly in such a moist environment. A synthetic resin film of ethylene trifluoride chloride or polyethylene is typically used for the protective sheet 6 of the transparent electrode, while a highly moisture-resistant metal composite film made of a pair of resin films 8, 8 of a material such as polyethylene terephtalate and a laminated metal 9 inserted therebetween is typically used as the protective sheet 7 for the opposite electrode 4. The peripheries of the two protective sheets 6 and 7 are bonded together by means of heat seal using a hot melt.
An ELD having a configuration as described above is typically used for a back light in a liquid crystal display apparatus. As shown in FIG. 5, ELD 20 is fitted to the back of the casing 22 incorporating a liquid crystal display 21 by utilizing a fixture 23 of the casing 22 and then the casing 22 is rigidly mounted on a wiring circuit substrate 24, while said liquid display 21 and ELD 20 are electrically connected with a drive circuit in said wiring circuit substrate 24 so that the light emitted from the light emitting layer 3 of the ELD 20 functions as a back light of the liquid crystal display 21 of a transmission type. Reference numeral 10 in FIG. 5 denotes a lead terminal for an external source to be connected with the ELD 20 and numeral 11 denotes a fitting bore to accommodate the fixture 23.
While a conventional ELD as described above and using a metal composite film 7 as a protection sheet for the opposite electrode 4 can be highly moisture-resistant because of the use of a metal laminate 9, it requires some electric insulating measures because it can undesirably affect circuits external to the ELD as the periphery of the metal foil 9 is exposed to the atmosphere and therefore can become electrically active. Referring to FIG. 5, if the casing 22 is made of a metal sheet with a view of giving it a function of grounding, noises picked up by the metal foil 9 can proceed to the grounding to interfere with the normal operation of the drive circuit because the metal foil 9 is connected with the metal fixture 23 within the fitting bore 11.
It is therefore an object of the present utility design to provide an ELD which uses a metal composite film for the protective sheet but effectively eliminates adverse effects of the metal film to external circuits.